iPhone 11 volume not working and only vibrates

On an iPhone, Media Volume, Alarm Volume, Alert/Ringer Volume, and Call Volume are related but not all controlled by the same setting. 

1. Media Volume

This controls the sound produced by apps and media, such as:

YouTube and other videos

Music

Games

Podcasts

Most app sounds

Audio played through the iPhone speaker, headphones, CarPlay, Bluetooth, etc.

How to control it:

Press the Volume Up/Down buttons while media is playing, or

Open Control Center and move the volume slider.

The volume buttons normally control media volume when you are actively playing media.

2. Ringer / Alert Volume

This controls sounds such as:

Incoming phone calls

Text/message notifications

Mail notifications

App notification sounds

Calendar/reminder alerts

Other system alert sounds

Go to: Settings → Sounds & Haptics → Ringtone and Alerts

The Ringtone and Alerts slider controls this group of sounds.

You can also enable Change with Buttons. When enabled, the physical volume buttons can change the ringtone/alert volume when you're not actively controlling media.

Important: Turning media volume down to zero does not necessarily turn notification/ringer volume down to zero.

3. Alarm Volume

This is where there is an important distinction.

For Apple's Clock app alarms, the alarm volume is generally tied to the Ringtone and Alerts volume.

So if you set:

Settings → Sounds & Haptics → Ringtone and Alerts → 50%

your normal Clock alarm will use that level.

Changing the volume of a YouTube video, for example, doesn't change the Clock alarm volume.

Also, the Silent Mode switch does not silence a normal Clock alarm. That's intentional—otherwise it would be rather easy to sleep through an alarm.

4. Call Volume

There are actually two different "call volumes."

A. Volume of the person you're talking to

During a phone call, the side volume buttons control the volume of the other person's voice coming through the earpiece or speaker.

This is separate from your normal media volume.

For example:

You are listening to YouTube → volume at 70%

You make a phone call → you set call volume to 40%

Changing the call volume doesn't necessarily change your YouTube volume.

B. Ringtone volume

Before you answer a call, the incoming ringtone uses the Ringtone and Alerts volume described above.

Once you answer, the volume buttons control the call audio.

One particularly important iPhone setting

Go to: Settings → Sounds & Haptics → Ringtone and Alerts

You'll see the Ringtone and Alerts slider.

Below/around it you'll also find Change with Buttons.

If Change with Buttons is OFF, the physical volume buttons generally won't accidentally change your ringtone/alert volume when you're not playing media.

If Change with Buttons is ON, pressing the volume buttons when you're not actively playing media can change the ringtone/alert level.

So, if you want your alarm and notifications to remain at a fixed level, while freely using the side buttons for YouTube/music, keeping Change with Buttons OFF is usually the better arrangement.

If any Focus mode is enabled, notifications from certain apps may be delayed or suppressed, depending on your Focus settings. In some cases, you may not receive a notification until you manually open the app. Check whether a Focus mode is active and review its notification settings to ensure the app is allowed to send notifications.

Then please check the following.

1. Check your DND status - Settings > Focus [Do Not Disturb]; Use Focus on your iPhone, iPad, or iPod touch - Apple Support
2. Three primary factors trigger the automatic activation of the Focus modes. Users have the flexibility to deactivate each of these factors based on their individual preferences. 
   1. Automatic Activation: Driving, Fitness, Gaming, Mindfulness
   2. Smart Activation: Work, Reading, DND
   3. Scheduled Activation: DND, Gaming, Mindfulness, Personal, Reading, Sleep, Work, Fitness
   4. Here are comprehensive explanations for each of these three triggers. --> Unveiling the Multi-Faceted Triggers of DND Automatic… - Apple Community
3. Check Bedtime Status - Clock App; Use Bedtime to track your sleep on your iPhone - Apple Support
4. Check your iPhone Sound Volume; Adjust the volume on your iPhone - Apple Support
5. Check Call Audio Routing; Call Audio Routing Bluetooth / Speaker / Automatic
6. Check Auto Answer Calls; Turn off Auto Answer Calls
7. Check the list of Blocked Numbers --> Block phone numbers, contacts, and emails on your iPhone ...

Notification Preview when Screen is Locked, Notification Alerts, Notification OFF, and much more...

1. To get Notifications when the Screen is locked see the pic below which is self-explanatory
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2. To turn ON notifications selectively for apps, go to Settings > Notifications > Scroll Down to the App and turn ON notifications... Change notification settings on iPhone - Apple Support (IN)
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3. Some apps have their own notification settings over and above the iOS notification settings: An example of Instagram Notification settings is given below
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4. Help for Notification Alerts --> No Notification Alerts - Apple Community
5. For VIP email Alerts refer to the pic below
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6. The pic below is self-explanatory
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